Fluid pressure servomotors



Aug 17, 1965 'R. A. L. THIRION FLUID PRESSURE SERVOMOTORS Filed March 1, 1963 INVENTOR. 251v: A. 1.. rule/0;

United States Patent Office Biddfij Patented Aug. 17, 1965 3 5 Claims. rcr. 601tl.5)

The present invention relates to fluid pressure servomotors and more particularly to control valves for servomotors of the type comprising a first chamber connected to one of the variable volume compartments of the servomotor and to a first source of fluid pressure, a second chamber connected to the other compartment of the servomotor, and a third chamber connected to a second source delivering fluid under a pressure different from that of the first source, said first and second chambers being separated by a reaction diaphragm connected to the valve actuating member and provided with an opening controlled by a first valve member attached to a second valve member controlling another opening formed in a wall segregating the second and third chambers, these valve members being so arranged that the first valve member can only open after the second valve member has closed and vice versa.

In the inoperative condition of the servomotor one of the valve members is held closed by a spring and the other valve member is open. As the valve members are placed in various chambers of the control valve the sum of the pressure forces acting on the movable assembly formed by the two valve members is different from zero, and it will be necessary to overcome this pressure force to operate the control valve. For the same reason when a determined force is exerted on the actuating member of the control valve and the power piston of the servomotor is held by fluid pressure differential in a determined position, and thereafter the force on the valve actuating member is decreased to cause the power piston of the servomotor to move backwardly, the backward movement of the power piston will take place only after the force on the valve actuating member has been substantially reduced; this phenomenon is called hysteresis. These drawbacks are particularly detrimental when the servomotor is used in a braking system.

The object of the present invention is to eliminate these drawbacks by providing a balanced movable assembly in the control valve of the servomotor. This object is achieved by attaching the second valve member to a flexible wall which separates the third chamber of the control valve from a fourth chamber which communicates with the first chamber, the area bounded by the seats of the two valve members and the effective area of the flexible wall being equal.

The features of the invention and the attendant advantages will more fully appear from the following description whichrefers to the accompanying drawing which shows a fluid pressure servomotor made in accordance with the invention and adapted to be used in a braking system.

The servomotor shown in the drawing is vacuum suspended and comprises a two-part housing 12 divided into two compartments 14 and 16 by a power piston formed of a flexible diaphragm 18 having its periphery clamped between the edges of the two housing parts. The diaphragm 18 lies over a cup 20 made of metal sheet and secured to the end of a rod 22 which is adapted to displace the piston 24 of a slave hydraulic cylinder 26. The cylinder 26 is formed in a casting comprising a cylindrical portion 30 extending in the compartment 14 and sealingly secured to the housing 12 by means of a flange 28. A

guide bearing 32 is retained in a bore 34 formed in the portion 3% by a washer 36 and a stop ring 38 and serves to guide and support the rod 22. An annular seal at having a U-shaped cross section is fitted in the bore 34 and sealingly engages the outer surface of the rod 22, and a ring 22, which abuts a shoulder formed at the inner end of the bore 34, presses the seal 40 against the end face of the bearing 32.

The hollow piston 24 slides in a bore 44 of the hydraulic cylinder 26. The rod 22 extends into the piston 24 and is connected thereto by means of a cross pin 46 having its ends received in oversized holes formed in the wall of the piston, whereby a lost-motion connection is provided between the rod and piston.

The piston 24 is normally biased against the ring 42 by a return spring 48 compressed between the bottom of the housing 12 and the cup 20.

The hydraulic fluid supplied by a master-cylinder, not shown, is communicated to the space behind the piston 24 through an inlet port 59, and the hydraulic pressure acts in addition to the force of the servomotor to displace the piston 24 in the bore 44'. The hydraulic fluid in the bore 44 is forced by the piston 24 in the hydraulic circuit of the braking system through opening 52. To keep the hydraulic circuit of the braking system connected to the cylinder 26 full of hydraulic fluid a passage 54 is provided in the piston 24 to communicate the inlet port 50 to the portion of the bore 44 in front of piston 24 when the latter is in its rest position, as shown in the drawing.

The rod 22 carries at its end a ball 56, which closes the passage 54 when the rod is moved towards the right to disconnect the inlet port 56 from the portion of bore 44 located in front of piston 24.

The servomotor 10 comprises a control valve 6i made in accordance with the invention and which controls the pressure differential acting on the diaphragm 18. The servomotor 10 is of the vacuum suspended type in which vacuum exists on both sides of the diaphragm 18 when the servomotor is at rest and in which atmospheric air is admitted in compartment 16 when operation of the servomotor is desired. Compartment 14 communicates through a passage 62 with a chamber 64 of the control valve and is permanently connected to a vacuum-source. The control valve comprises further a control chamber 66 which is permanently connected to the compartment 16 of the servomotor by means of conduit 63, and a chamber 70 which communicates with atmosphere through passages 72, atmospheric air being admitted in chamber 70 through a filter element 74 housed in a cap 76. Chamber 64 is formed in a boss 77 of the casting in which is formed the cylinder as, and is separated from chamber 66 by a reaction diaphragm 78 made of rubber or rubber-like material. Chamber 66 is separated from chamber 7%) by a rigid wall 550 of a casing 82 in which are formed chambers 66 and 7t and which is attached to boss 77 by screws 84 which also serve to secure cap 76.

The wall is formed with an opening $6 which communicates chambers 66 and 70. The edge of diaphragm 78 is sealingly clamped between the edges of boss 77 and casing 82. A tubular member 88 which communicates chambers 64 and 66 is attached to diaphragm 78 generally coaxially of opening 86. Diaphragm 78 comprises a tubular portion 90 surrounding the base of tubular member 38 and extending slightly beyond the end thereof so as to form an annular seat for a valve member 92 having a tail portion 94 which extends into chamber 79 through opening 86. The end of tail 94 is embedded in a rubber block 96 which forms a second valve member controlling opening 86. A flexible wall 93, which is made integral with block 96, forms the bottom of chamber 70, the edges of this wall being sealingly clamped between the casing 82 and the cap '76. An axial passage 10% is provided in the tail of valve member 92 and in the block 96 to communicate the chamber 102 defined by the wall 9% and cap 76 to chamber 64 or 66 according to the position of valve member 92. The area bounded by the seats of valve members 92 and 96 and the effective area of wall 98 are equal, so that the sum of the pressure forces acting on the movable assembly formed of valve member 92 and 96 and wall 98 is always'zero. In the non-operative condition of the servo-motor the valve member 96 is biased against the wall 34 by the resilient wall Q8, and the diaphragm '78 is urged towards chamber (Ed by a spring 16% which biases the tubular member 88 against a shoulder 1%.

The tubular member 88 is formed integral with a piston 11% slidably received in a bore 1% which is communicated to the portion of bore 44 located behind piston 24- and consequently to inlet port 50.

The operation of the servomotor is as follows: At rest the various parts of the servomotor are in the positions shown in the drawing. When a hydraulic fiuid supplied by a master cylinder, not shown, is delivered to inlet port Sit, the piston lllli) and tubular member $8 are displaced by the hydraulic pressure and the tubular portion 99 of diaphragm '78 is moved into engagementwith valve member 92 and thereby closes the communication between compartment'lti of the servomotor and the vacuum source. Thereafter valve member 96 is moved away from wall Sit and atmospheric air is allowed to flow in chamber 65 of the control valve and then to compartment 16 of the servo- .iotor. Since the movable assembly 92, 96, 98 is balanced the force required to produce'this initial movement of the movable assembly is very small, as it is equal to the sum of the force of spring 1M and of resiliently deformable wall 93 and of the force due to atmospheric pressure acting on the piston 11%) through the intermediary or" the hydraulic fluid, while in conventional servomotors it is necessary to overcome in addition, the action of pressure forces on both valve members. hereby the time delay in initiation of servomotor operation is very much reduced.

The increase in pressure in compartment 16 of the servomotor causes the diaphragm 18 to move and drive the rod 22. The ball 56 of rod 22 then closes the passage 54 to disconnect the portion of bore 44 in front of piston 24 from inlet port h. The piston 24 is then displaced in bore 44 by the rod 22, and the hydraulic fluid pressurized in the bore 4-4 is forced in the hydraulic circuit of the braking system through opening 52. As long as the valve member 96 is held apart from wall 8% the pressure in chamber as increases and exerts on diaphragm 78 an increasing force which acts against the force exerted on piston lit) by the pressure of the hydraulic fluid supplied to inlet port Sit. When the pressure at the inlet port 59 is kept at a constant value the diaphragm 78 is moved towards chamber 6 until valve member 96 closes opening 86; then the pressure in compartment 16 of the servomotor increases no more and the diaphragm 18 stops.

When it is desired to reduce the braking effort the pressure at the inlet port 50 is reduced whereby the pressure forces acting on the diaphragm 78rnoves the tubular portion 9t thereof away from valve member )2, the compartment to is then communicated tothe vacuum source and the pressure in this compartment decreases whereby the hydraulic pressure in the bore 44 and the return spring 23 moves the piston 24 baclrwardly. It must be noted that diaphragm 78 moves away from valve member 92 to communicate chambers 64 and as as soon as the pressure at inlet port 59 decreases, even very slightly, while in conventional servornotors the pressure at the inlet port must be reduced by an amount corresponding to the pressure forces on the valve members before the diaphragm moves-and the piston of the servomotor initiates its backward movement.

As pressure in chamber 66 decreases diaphragm '78 moves away from chamber 64 until the portion of the diaphragm engages valve member 92; then the pressure in chamber 16 decreases no more and piston 24 stops.

When the pressure at the inlet port 50 is decreased down to atmospheric pressure the diaphragm 78 is moved towards chamber 64 until the tubular member 38 abuts shoulder 166. Compartment 16 is then communicated to the vacuum source, and the pressures acting on the sides of the diaphragm 18 being then equal, the spring 48 returns the piston 24 in its rest position. After the piston 24 abuts the ring 42, the ball 56 is moved away from the opening of passage 54, and the portion of bore 44 in front of piston 24 is then communicated to inlet opening 56 whereby pressures equalize in the whole hydraulic circuit.

Although the invention has been herein described in its application to a vacuum actuated servomotor for a braking system, it is obvious that the described valve can be used in various types of fluid pressure servomotors. It is also possible to modify the described valve structure to adapt it to the use for which it is designed, and it is obvious that such modifications are within the scope of the invention. 7 a

What is claimed is:

1. In a fluid pressure 'servomotor having a housing divided into two compartments by a power piston, a control valve for controlling the operation of the servomotor, said control valve comprising a casing, a first chamher in said casing connected to one of the compartments and to a first source of fluid pressure, a second chamber connected to the other of the compartments, said first and second chambers being separated by a fluid pressure responsive member operatively connected'to a valve actuating member, a third chamber connected to a second source of fiuid pressure delivering fluid at a' pressure differing from that of the first source and a movable valve assembly formed of a first valve member controlling the communication between said second and third chambers and having a tail portion which is embedded in a block of rubber or rubber-like material forming a second valve ember controlling the communication between said second and third chambers, said block being formed integral with a flexible annular wall which separates said third chamber from a fourth chamber communicating with said first chamber the areas bounded by the seats of said first and second valve members and the efiective area of said flexible wall being equal.

2. In a pneumatic servomotor having a housing divided into two compartments by a power piston, a control valve for controlling the operation of the servomotor, said control valve comprising;

a housing having a chamber in fluid communication with one of the compartments of the servomotor;

a movable wall in said chamber of said housing dividing said chamber into a first variable volume chamber and a second variable volume chamberwhich first variable volume chamber is arranged to be in fluid communication with the one compartment of the servomotor and with a fiuid pressure source with the second variable volume chamber in fluid communication with the other chamber of the servomotor, said movable wall'beingprovided with an annular valve seat about an axial passage therethrough which communicates said first and second variable volume chambers;

a means within said second chamber 'for dividing said second chamber into a first andsecond portion, said meansbeing provided with an opening for communieating said first and second portions of said second variable volume chamber; and

a movable valve assembly operatively connected within said means in said second variable volume chamber. and arranged to control the opening in said means, said movable valve assemblyincluding,

a first valve member operatively arranged to cooperate with said annular valve to control the communication between said first and second variable volume chambers,

a second valve member attached to said first valve member arranged to control the opening in said means dividing said second chamber into a first and second portion, and a resilient flexible wall attached to said second valve member and said means dividing said second variable volume chambers into first and second portions so that said flexible wall divides the second portion into third and fourth variable volume chambers which third variable volume chamber is communicated to a second source of fluid pressure differing from that of said first source and said fourth variable volume chamher is communicated by means of an axial passage through said movable valve assembly to the first portion of said variable volume chamber so long as said movable valve assembly is spaced from said annular valve and when said annular valve is in contact with said movable valve assembly said passage communicates with said first fluid pressure source, the areas of said first and second valve members and the effective area of said flexible wall being equal. 3. A pnumatic servomotor as defined in claim 2, in which the peripheral edge of said resilient flexible wall is clamped between a cap and an end surface of the I cylindrical portion of the valve housing.

4. In a hydraulic pressure intensifying unit having a master cylinder, a slave cylinder, a piston in said slave cylinder adapted to be displaced by the power piston of a fluid pressure motor that is divided into two variable volume compartments, a control valve for controlling the operation of the fluid pressure motor at the direction of a fluid pressure that is generated by the master cylinder, said control valve comprising:

a housing having a chamber therewithin which is communicated by means of appropriate passages to one of the compartments and a first source of fluid pressure for the fluid pressure motor;

a fluid pressure responsive member operatively connected to the housing and to a piston responsive to pressure being generated by the master cylinder, said fluid pressure responsive member dividing the chamber of said housing into a first variable volume chamber and a second variable volume chamber with the first variable volume chamber being open to the fluid pressure source and the second variable volume chamber being communicated by means of a conduit to the other of the two variable volume compartments of the fluid pressure motor;

an end structure containing a third chamber connected to a second source of fluid pressure delivering fluid at a pressure diifering from that of the first source which end structure is connected to said housing; and

a movable valve assembly operatively connected to said end structure and including,

a first valve member controlling the communication between said first and second variable volume chambers,

a second valve member attached to said first valve member and controlling the communication between said second variable volume chamber and said third chamber, and

a resilient flexible wall operatively connected to said second valve member and arranged to bias said second valve member to prevent communication between said second variable volume chamber and said third chamber, said resilient flexible wall dividing said third chamber into a fourth variable volume chamber and a fifth variable volume chamber, said first and second valve members having annular valve seats the area bounded by which is equal to the effective area of said resilient flexible wall, and said movable valve assembly being provided with a centrally located passage to communicate said second variable volume chamber and said fifth variable volume chamber until communication between said first and second variable volume chambers has been terminated and thereafter to communicate said first variable volume chamber and said fifth variable volume chamber.

5. A pressure intensifying unit as defined in claim 4 in which said first valve member has a tail portion which is embedded in a block of rubber or rubber-like material which forms said second valve member, and said flexible wall is made integral with said block.

References Cited by the Examiner UNITED STATES PATENTS 3,082,745 3/63 Brooks 91369 3,099,941 8/63 Helvern et a1. 91-434 3,113,806 12/63 Cripe 54.6 X

JULIUS E. WEST, Primary Examiner. ROBERT R. BUNEVICH, Examiner. 

1. IN A FLUID PRESSURE SERVOMOTOR HAVING A HOUSING DIVIDED INTO TWO COMPARTMENTS BY A POWER PISTON, A CONTROL VALVE FOR CONTROLLING THE OPERATION OF THE SERVOMOTOR, SAID CONTROL VALVE COMPRISING A CASING, A FIRST CHAMBER IN SAID CASING CONNECTED TO ONE OF THE COMPARTMENTS AND TO A FIRST SOURCE OF FLUID PRESSURE, A SECOND CHAMBER CONNECTED TO THE OTHER OF THE COMPARTMENTS, SAID FIRST AND SECOND CHAMBERS BEING SEPARATED BY A FLUID PRESSURE RESPONSIVE MEMBER OPERATIVELY CONNECTED TO A VALVE ACTUATING MEMBER, A THIRD CHAMBER CONNECTED TO A SECOND SOURCE OF FLUID PRESSURE DELIVERING FLUID AT A PRESSURE DIFFERING FROM THAT OF THE FIRST SOURCE AND A MOVABLE VALVE ASSEMBLY FORMED O A FIRST VALVE MEMBER CONTROLLING THE 